Method and apparatus for substrate temperature control

ABSTRACT

A method and apparatus for gas control is provided. The apparatus may be used for controlling gases delivered to a chamber, controlling the chamber pressure, controlling the delivery of backside gas between a substrate and substrate support and the like. In one embodiment, an apparatus for controlling gas control includes at least a first flow sensor having a control valve, a first pressure sensor and at least a second pressure sensor. An inlet of the first flow sensor is adapted for coupling to a gas supply. A control valve is coupled to an outlet of the flow sensor. The first pressure sensor is adapted to sense a metric indicative of the pressure upstream of the first flow sensor. The second pressure sensor is adapted to sense a metric indicative of the pressure downstream of the control valve.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional patent applicationSer. No. 60/527,428, filed Dec. 4, 2003, which is herein incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to a method andapparatus for controlling pressure and measuring flow. Morespecifically, embodiments of the invention generally relate to a methodand apparatus for controlling gas provided between a substrate and asubstrate support in a semiconductor processing chamber or to asemiconductor processing chamber.

2. Description of the Related Art

Substrate temperature is an important process control attribute criticalto many microelectronic device fabrication processes. Providing gasbetween the substrate and a substrate support in a semiconductorprocessing chamber is a well-known method for improving heat transferbetween the substrate and the substrate support, thereby enhancing theprecision and uniformity of substrate temperatures.

FIG. 1 depicts a simplified schematic of a conventional semiconductorprocessing chamber 150 having a gas delivery system 100 shown providingbackside gas between a substrate 154 and a substrate support 152disposed in the processing chamber 150. The processing chamber 150 maybe configured to perform chemical vapor deposition (CVD), physical vapordeposition (PVD), etch chamber or other vacuum processing technique.Process gas delivery systems, pumping systems and the like forcontrolling processes performed within the processing chamber arewell-known and have been omitted for the sake of brevity.

The substrate support 152 generally includes a passage 156 formedtherethrough for delivering a heat transfer gas (hereinafter referred toas backside gas) to an area 158 defined between the substrate 154 andsubstrate support 152. The size of the area 158 has been exaggerated forclarity. The backside gas, such as helium or another gas is generallyprovided by the gas delivery system 100.

The gas delivery system 100 located outside the processing chamber 150and includes a gas supply 104 and control circuit 102. The delivery ofbackside gas from the supply 104 to the area 158 is regulated by acontrol circuit 102. A shut-off valve 106 is generally provided betweenthe supply 104 and control circuit 102.

The control circuit 102 generally includes a thermal flow sensor 110,control valve 112, a pressure sensor 114 and a restrictor 118. An inletline 120 is coupled to an inlet of the flow sensor 110 and facilitatescoupling the control circuit to the shut-off valve 106. A firstintermediate line 122 couples an outlet of the flow sensor 110 to thecontrol valve 112. A second intermediate line 124 couples an outlet ofthe control valve 112 to an outlet line 126. The outlet line 126facilitates coupling the control circuit 102 to the passage 156 to thatgas provided by the supply 104 may be delivered in a regulated manner tothe area 158 between substrate 154 and substrate support 152. A pressuresensor 114 is coupled to the second intermediate line 124 and is adaptedto provide a metric of pressure of the gas within the secondintermediate line 124.

A bypass line 128 is teed into the outlet line 126 and is coupled to avacuum source 116. A restrictor 118, such as a needle valve, is providedin series with the bypass line 128 to regulate the flow therethrough.

In operation, the control circuit 102 is set to a predefined pressuremeasured by the pressure sensor 114. The flow sensor 110 measures theflow of gas to the control valve 112. The control valve 112 is modulatedin response to pressure variations as detected by the pressure sensor114, such that the pressure of gas delivered to the area 158 between thesubstrate 154 and the substrate support 152 is provided at a predefinedpressure.

Although this design has proven to control pressure in this application,field experience with the existing technology has increased the demandfor more accurate measurement of flow. In addition accelerated responseto change in pressure set points is needed to reduce process cycletimes. For example, gas temperature and/or pressure fluctuationsupstream of the gas delivery system may make the flow through the flowsensor unstable, thereby reducing the accuracy of the correlationbetween the flow indicated and the actual flow to both the area betweenthe substrate and substrate support and the restrictor. Additionally,variation in the vacuum provided by the vacuum source may impact theflow through the restrictor, which may falsely indicate or contribute toerroneous interpretation of the amount of gas disposed between substrateand substrate support. In critical applications, the gas available as aheat transfer medium between the substrate and substrate support mayvary, leading to deviation in substrate to substrate processperformance.

In addition, the system as described in FIG. 1 is unable to determinethe rate of gas flowing into the area between the substrate support andsubstrate or to determine small variations in the rate of gas leakagebetween the substrate support and substrate that may cause the heattransfer characteristics and uniformity to vary, thereby resulting inunwanted variation in processing performance. Thus, it would bedesirable to know in addition to pressure the rate of gas flow to thesubstrate support.

Therefore, there is a need for an improved method and apparatus forcontrolling the delivery of backside gas in a semiconductor processingsystem.

Chamber pressure control is an equally important process controlattribute. Throttle valves are typically placed between the chamber anda vacuum pump to control chamber pressure. In these applications achamber pressure gage provides feedback to the throttle valvecontroller. However in an application where the conductance between thethrottle valve and the chamber is much smaller then the controllableconductance of the throttle valve, it is not possible to control chamberpressure with a throttle valve between the chamber and a vacuum pump.Therefore, there is a need for a method and apparatus for controllingthe delivery of gas into a chamber such that the delivery rate resultsin the desired chamber pressure.

SUMMARY OF THE INVENTION

A method and apparatus for gas control is provided. The method andapparatus may be used for controlling gases delivered to a chamber,controlling the chamber pressure, controlling the delivery of backsidegas between a substrate and substrate support and the like. In oneembodiment, an apparatus for controlling gas control includes at least afirst flow sensor having a control valve, a first pressure sensor and asecond pressure sensor. An inlet of the first pressure sensor is adaptedfor coupling to a gas supply. A control valve is coupled to an outlet ofthe flow sensor. The first pressure sensor is adapted to sense a metricindicative of the pressure upstream of the first flow sensor. A secondpressure sensor is adapted to sense a metric indicative of the pressuredownstream of the control valve.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a simplified schematic of a conventional semiconductorprocessing chamber and gas delivery system;

FIG. 2 is a simplified schematic of one embodiment of a gas deliverysystem of the invention coupled to an exemplary a semiconductorprocessing chamber;

FIG. 3 is a simplified schematic of another embodiment of a controlcircuit of a gas delivery system coupled to a processing chamber;

FIGS. 4-6 are simplified schematics of alternative embodiments of a gasdelivery system; and

FIGS. 7-8 are simplified schematics of alternative embodiments of acontrol circuit.

To facilitate understanding, identical reference numerals have beenused, wherever possible, to designate identical elements that are commonto the figures.

DETAILED DESCRIPTION

FIG. 2 depicts a simplified schematic of one embodiment of a gasdelivery system 200 of the invention coupled to an exemplary asemiconductor processing chamber 150. As described above, the processingchamber 150 includes a substrate support 152 disposed therein whichsupports a substrate 154 during processing. The processing chamber 150may be configured to perform chemical vapor deposition (CVD), physicalvapor deposition (PVD), etch chamber or other vacuum processingtechnique. Process gas delivery systems, pumping systems and the likefor controlling processes performed within the processing chamber arewell-known and have been omitted for the sake of brevity.

The substrate support 152 generally includes a passage 156 formedtherethrough for delivering a heat transfer gas (hereinafter referred toas backside gas) to an area 158 defined between the substrate 154 andsubstrate support 152. The size of the area 158 has been exaggerated inFIG. 2 for clarity. The backside gas, such as helium, nitrogen, argon oranother gas is generally provided by the gas delivery system 200.

The gas delivery system 200 is located outside the processing chamber150 and includes a gas supply 104 and a control circuit 202. Thedelivery of backside gas from the supply 104 to the area 158 isregulated by the control circuit 202. At least one shut-off valve 106 isprovided between the supply 104 and the control circuit 202. It iscontemplated that the shut-off valve 106 may be an integral part of thecontrol circuit 202.

The control circuit 202 generally includes a first pressure sensor 290,a second pressure sensor 214 (optional), a flow sensor 210, controlvalve 212, a third pressure sensor 216, and a bypass control branch 218.It is contemplated that the control circuits described herein may bereadily adapted for use in other applications, such as chamber pressurecontrol, process gas delivery and the like.

An inlet line 220 is coupled to an inlet of the flow sensor 210 andfacilitates coupling the control circuit 202 to the shut-off valve 106.The flow sensor 210 provides a metric indicative of flow F_(S) passinginto the control circuit 202. The flow sensor 210 may be a thermal basedtechnology (most common), a delta pressure based technology, a correolistechnology, or any other technology capable of providing mass flow rate.The first pressure sensor 290 is coupled to the inlet line 220 and isadapted to provide a metric indicative of the pressure P_(U) upstream ofthe flow sensor 210. The first pressure sensor 290 can be used to ensurethat the output of the flow sensor 210 during upstream pressureperturbations accurately reports the flow through the flow sensor 210.

A first intermediate line 222 couples an outlet of the flow sensor 210to the control valve 212. The first intermediate line 222 has apredetermined volume V_(S). The predetermined volume V_(S) may becalculated or measured. The optional second pressure sensor 214 iscoupled to the first intermediate line 222 and is adapted to provide ametric indicative of the pressure P_(S) within the volume V_(S).

A second intermediate line 224 couples an outlet of the control valve212 to an outlet line 226 of the control circuit 202. A supply line 228couples the outlet line 226 to the passage 156 and allows gas, regulatedby the control circuit 202, to be delivered to the area 158 betweensubstrate 154 and substrate support 152.

The bypass control branch 218 includes a restrictor 230 and a bypassvalve 232 coupled in parallel. A bypass inlet line 234 is teed tojunction of the second intermediate line 224 and outlet line 226, and iscoupled to the inlets of the restrictor 230 and the bypass valve 232. Abypass outlet line 236 couples the outlets of the restrictor 230 and thebypass valve 232 to a vacuum source 116. The restrictor 230 is set orselected to have a predefined orifice such that a chocked condition isachieved where P_(W) (described below) is greater than 2 times thevacuum provided by the vacuum source 116. The restrictor 230 may befactory set to this condition, or set on site by a technician or tooloperator. With the restrictor 230 set to this condition, P_(W) sensed bythe pressure sensor 216 is also indicative of the pressure in the area158 below the substrate 152.

The bypass valve 232 may be opened to allow quick evacuation andpressure drop within the control circuit 202. This allows for quickreductions in pressure Pw to be realized in a short amount of time andas a result significantly reduce process times associated with longdelays that are required with the existing technology.

A predetermined control volume V_(W), defined by the gas conduits with adashed line 240, includes the volumes of the second intermediate line224, the bypass inlet line 234, the outlet line 226, the supply line228, the passage 156 and the area 158. The control volume V_(W) may becalculated or measured. The third pressure sensor 214 is coupled to atleast one of the gas conduits comprising the control volume V_(W) and isadapted to provide a metric of pressure P_(W) of the gas within thecontrol volume V_(W). In the embodiment depicted in FIG. 2, the thirdpressure sensor 214 is coupled to the second intermediate line 224.

To facilitate control of the control circuit 202 as described above, acontroller 260 comprising a central processing unit (CPU) 262, supportcircuits 266 and memory 264, is coupled to the control circuit 202. Thecontroller 260 may additionally control processes performed in theprocessing chamber 150. The CPU 262 may be one of any form of computerprocessor that can be used in an industrial setting for controllingvarious chambers and subprocessors. The memory 264 is coupled to the CPU262. The memory 264, or computer-readable medium, may be one or more ofreadily available memory such as random access memory (RAM), read onlymemory (ROM), floppy disk, hard disk, or any other form of digitalstorage, local or remote. The support circuits 266 are coupled to theCPU 262 for supporting the processor in a conventional manner. Thesecircuits include cache, power supplies, clock circuits, input/outputcircuitry, subsystems, and the like.

In operation, a desired pressure set point P_(W) is selected. The flowsensor 210, and pressure sensors 290, 214, and 216 respectively providea metric of flow and pressure to the controller 260.

As the volumes V_(S) and V_(W) are known for the volumes correspondingto the pressure sensed by the pressure sensors 214, 216, a flow F_(A) ofgas the flow to area 158 between the substrate 154 and substrate support152 and through the bleed restrictor 230 may be expressed as:$\begin{matrix}{F_{A} = {F_{S} + {F_{\Delta\quad P_{S}}\left( {\frac{\mathbb{d}P_{S}}{\mathbb{d}t},V_{s}} \right)} - {F_{\Delta\quad P_{W}}\left( {\frac{\mathbb{d}P_{W}}{\mathbb{d}t},V_{W}} \right)} - {F_{deltaP}\left( \frac{\mathbb{d}P_{U}}{\mathbb{d}t} \right)}}} & (1)\end{matrix}$andF _(W) =F _(A) F _(BLEED)(P _(W))  (2)where:

-   F_(BLEED) is the flow through the bypass outlet line 236 (typically    factory calibrated as a function of Pw),-   F_(W) is the flow measured to the area 158 between the substrate 154    and substrate support 152 through the outlet line 226 of the control    circuit 202, and-   F_(A) is the flow measured by the flow sensor 210; and-   in embodiments where a second pressure sensor is not utilized,    F_(ΔPw)(dP_(w)/dt, V_(W) is zero.

Knowing F_(W) and P_(W) provides more accurate characterization of theheat transfer conditions between the substrate 154 and substrate support152. The leak rate of backside gas from under the substrate 154 can nowbe quantified and associated with process conditions such as heattransfer uniformity, substrate chucking characteristics and wear of thesubstrate support.

FIG. 3 is a simplified schematic of another embodiment of a controlcircuit 302 of a gas delivery system 300 coupled to a processing chamber350. The control circuit 302 has a plurality of outlet lines 312 _(i)thereby enabling control of multiple gas flows from a single controlcircuit 302. The subscript “i” used herein is a positive integer. Thegas delivery system 300 is similar to the system 100 described above,having a gas supply 104, a shut-off valve 106 and a vacuum source 116.

The processing chamber 350 is similar to the processing chamber 150described above, except wherein a substrate support 352 disposed in theprocessing chamber 350 includes multiple zones 360 _(i) of backside gaspressure control. Each zone 360 _(i) defined in an area 358 between thesubstrate 154 and the substrate support 352 has gas supplied thereto byat least one of the outlet lines 312 _(i). In the embodiment depicted inFIG. 3, the substrate support 352 has two zones 360 ₀ and 360 _(i)supplied by output lines 312 ₀, 312 _(i).

The control circuit 302 includes a plurality of sub-circuits 310 _(i).The sub-circuits 310 _(i) are configured similar to the circuits 102described above and share the gas supply 104 and vacuum source 116. Itis contemplated that one or more of the sub-circuits 310 _(i) may adedicated gas supply and vacuum source. Each of the sub-circuits 310_(i) controls the flow through a respective outlet line 312 _(i). Ineach of the circuits 310 _(i), the conductance downstream of the bypasscontrol branch 218 (referring additionally to FIG. 2) must ensure P_(W)is 2 times greater than vacuum provided by the vacuum source 116 whenall the outlets lines 312 _(i) are at maximum flow or when all of thelines 312 _(i) are flowing to the vacuum source 116 through the bypassvalve 232.

The control circuit 202 may be coupled to multiple substrates supportsin other configurations. For examples, FIG. 4 depicts the controlcircuit 302 coupled to two processing chambers. Although one output line312 _(i) is shown coupled to each processing chamber 150, it iscontemplated that the processing chamber may include substrates supportshaving multi-zone backside gas delivery, as discussed with reference toFIG. 3. In such a configuration, the circuit 302 may be configured toprovide gas through multiple output lines 312 _(i) to each chamber.

In another example depicted in FIG. 5, the control circuit 302 may becoupled to a single processing chamber 550 having multiple processingregions 502. An example of a processing chamber available in thisconfiguration is a PRODUCER® processing chamber, available from AppliedMaterials, Inc., located in Santa Clara, Calif. In the embodimentdepicted in FIG. 5, one output line 312 _(i) is shown coupled to eachsubstrate support 554 disposed in each processing region 502. It iscontemplated that the substrates supports 554 may include multizonebackside gas delivery, as discussed with reference to FIG. 3. In such aconfiguration, the circuit 302 may be configured to provide gas throughmultiple output lines 312 _(i) to each substrate support. It iscontemplated that a first output line 312 _(i) may be teed to supply afirst zone in a predefined number of substrate supports, while a secondoutput 312 _(i) may be teed to supply a second zone in each of thesubstrate supports, wherein the substrate supports are disposed in thesame or different processing chambers.

FIGS. 6-8 depict alternative embodiments of control circuits. It iscontemplated that any of the control circuits described in FIGS. 6-8 mayinclude multiple sub-circuits as described with reference to FIG. 3, orbe coupled one or more substrate supports having one or more backsidegas zones as described with reference to FIGS. 4-5.

FIG. 6 is a simplified schematic of another embodiment of a gas deliverysystem 600 of the invention coupled to a processing chamber 150. Theprocessing chamber 150 has been described above.

The gas delivery system 600 includes a gas supply 104 and a controlcircuit 602. The delivery of backside gas from the supply 104 to thearea 158 between the substrate 154 and substrate support 152 isregulated by the control circuit 602. The control circuit 602 generallyincludes a flow sensor 610, control valve 612, a first pressure sensor690, a second pressure sensor 614, a third pressure sensor 616 and abypass control branch 218.

An inlet line 620 couples the inlet of the control valve 612 to theshut-off valve 106. A first intermediate line 622 couples an outlet ofthe control valve 612 to the flow sensor 610. The control valve 612 andflow sensor 610 may be similar to the control valve 216 and flow sensor210 described above.

The first pressure sensor 690 is coupled to the first intermediate line622 and is adapted to provide a metric indicative of the pressure P_(U)upstream of the flow sensor 610. The first pressure sensor 690 can beused to ensure that the output of the flow sensor 610 during upstreampressure perturbations accurately reports the flow through the flowsensor 610.

A second intermediate line (shown as portions 624 a, 624 b) couples anoutlet of the flow sensor 610 to an outlet line 626 of the controlcircuit 602. A supply line 228 couples the outlet line 626 to thepassage 156 and allows gas, regulated by the circuit 602, to bedelivered to the area 158 between substrate 154 and substrate support152.

A restrictor 642 separates the portions 624 a, 624 b of the secondintermediate line. The restrictor 642 may have a fixed or variableorifice, and generally provides sufficient back pressure to accommodatethe operational parameters of the flow sensor 610. As such, with someflow meters, use of the restrictor 642 may not be required.

The first portion 624 a couples the flow sensor 610 to the restrictor642. The first portion 624 a has a predetermined volume V_(S). Thepredetermined volume V_(S) may be calculated or measured. The secondpressure sensor 614 is coupled to the first portion 624 a of the secondintermediate line and is adapted to provide a metric indicative of thepressure P_(S) within the volume V_(S).

The second portion 624 b runs from the restrictor 642 to at tee joiningthe outlet line 626 and bypass control branch 218. The bypass controlbranch 218 includes a bypass inlet line 234 that couples the outlet line226 and second portion 624 b of the second intermediate line to theinlets of a restrictor 630 and a bypass valve 232. The bypass controlbranch 218 is configured and generally functions as described above.

A predetermined control volume V_(W), defined by the gas conduits with adashed line 240, includes the volumes of the second portion 624 b of thesecond intermediate line, the bypass inlet line 234, the outlet line626, the supply line 228, the passage 156 and the area 158. The controlvolume V_(W) may be calculated or measured. The second pressure sensor614 is coupled to the at least one of the gas conduits comprising thecontrol volume V_(W) and is adapted to provide a metric of pressureP_(W) of the gas within the control volume V_(W). In the embodimentdepicted in FIG. 6, the second pressure sensor 614 is coupled to thesecond portion 624 b of the second intermediate line.

In operation, a desired pressure set point P_(W) is selected and thevalve 106 is opened to provide a flow of gas from the supply 104 to thecontrol circuit 602. The flow sensor 610, and pressure sensors 690, 614,616 respectively provide a metric of flow and pressure to the controller260. The pressure sensors 690, 614, 616 upstream and downstream of thecontrol valve 612 prevent transient pressure changes upstream anddownstream of the flow sensor 610 or in V_(w) of the control valve 612from effecting the flow measurements provided by the flow sensor 610.

As the volumes V_(S) and V_(W) are known for the volumes correspondingto the pressure sensed by the pressure sensors 614, 616, a flow F_(A) ofgas through the second portion 624 b of the second intermediate line anda flow F_(W) of gas to the area 258 between the substrate support 252and the substrate 254 the may be determined using equations (1) and (2)as discussed above.

FIG. 7 is a simplified schematic of another embodiment of a gas deliverysystem 700 of the invention coupled to a processing chamber 150. Theprocessing chamber 150 has been described above and may be configured toinclude a chamber pressure sensor 704 that is adapted to provide ametric indicative of the actual pressure P_(C) within the chamber 150.The gas delivery system 700 shown in FIG. 7 for regulating chamberpressure, or the flow of gas into a process volume within the chamber,may also be configured to provide backside gas to the substrate supportwithin the processing chamber. The chamber pressure sensor 704 is notneeded at this location for back side cooling applications where theeffective restriction R_(W) between control circuit 702 and substrate254 or processing chamber 150 is relatively large and the actual flowF_(W/C) through the effective restriction R_(W) to the chamber 150 isrelatively small. In chamber pressure control P_(C) is needed when R_(W)is relatively small and F_(W/C) is relatively large and feedback to thecontrol valve 706 is provided from the chamber pressure sensor 704.

The gas delivery system 700 includes a gas supply 104 and a controlcircuit 702. The delivery of gas from the supply 104 to the chamber 150is regulated by the control circuit 702 based on feedback from thechamber pressure sensor 704. The. control circuit 702 generally includesa control valve 706, a flow sensor 710, an upstream pressure sensor 718,and may also require a downstream pressure sensor 720 and a primarypressure sensor 714.

An input line 716 couples the gas delivery system 702 to the shut-offvalve 106. The input line 716 is connected to the flow sensor 710 thatis adapted to provide a metric indicative of flow F_(W/CB)′ through theflow sensor 710 placed upstream of the control valve 706. In the chamberpressure control application this may be the sum of two or more sensorsand control valves and may require control of the ratio of thesesensors. In the embodiment depicted in FIG. 7, only one flow sensor 710and control valve 706 are shown.

A first pressure sensor 718 is provided upstream of the flow sensor 710and adapted to provide a metric indicative of a pressure P_(US). Thefirst pressure sensor 718 can be used to ensure the flow sensor outputduring upstream pressure perturbations so that accurate determination ofthe flow through the flow sensor 710 can be made.

A second pressure sensor 720 is provided downstream of and adjacent tothe flow sensor 710 and adapted to provide a metric indicative of apressure P_(DS). The second pressure sensor 720 may be necessary formeasuring the pressure if transient pressure changes in the volumeV_(DS) defined in a first intermediate line 740 connecting the flowsensor 710 and the control valve 706 (i.e. dP_(DS)/dt). In such acondition, the flow sensor output may not be equal to the actual flowthrough the restriction downstream of the flow sensor (i.e. the controlvalve 706).

The second intermediate line 742 couples an outlet of control valve 706to a tee between an outlet line 744 and the bypass control branch 218.The outlet line 744 is coupled through a passage to the chamber 150.

The primary pressure sensor 714 may be necessary to provide a metricindicative of a pressure P_(WB) of the flow within the outlet line 744.The output from the primary pressure sensor 714 may be necessary toaugment the flow sensor output, as transient changes in pressure withinVw will result in differences between Fw/cb′ and Fw/c.

The bypass control branch 218 includes a pressure sensor 708 is adaptedto provide a metric indicative of a pressure P_(B) downstream of thebleed restrictor R_(B) and the bypass valve 232. To reduce cost, thepressure sensor 708 may be optionally omitted and the pressure P_(B) isassumed to be <{fraction (1/2)}P_(WB).

The restrictor 230 provides the effective restriction R_(B) of bleedflow. The restrictor 230 is sized such that flow through the restrictor230 is chocked. The restrictor 230 may not be needed for the chambercontrol application where F_(W/C) is relatively large. F_(B) is the flowthrough the bypass control branch 218 to the vacuum source 116.

The control circuit 702 can be used to calculate a volume V_(W) definedas that volume between the chamber restriction Rw, the bypass controlbranch 218, and the control valve 706. If shut-off valves are added atall ports of the control circuit to isolate its internal volume and thetotal internal volume of the control circuit V₁ (as isolated by theseshut-off valves) is known. In this configuration the controller 260 mustrun through the following steps to determine V_(W):

-   Step 1: Pressurize the control circuit;-   Step 2: Isolate the control circuit volume from the inlet pressure    source;-   Step 3: Open the shut-off valve on the w/c port. Note: A valve at    the chamber must be added and closed during this operation; and-   Step 4: After pressure in the control circuit volume has stabilized,    V_(W) may be expressed as V_(W)=(V₁(P₁/P₂−1))−sum of: volume between    the bleed restriction/dump valve and bleed port shut off valve;    volume between the first restrictor upstream of P_(WB), and the    supply port shut off valve.

The control valve must be open during this routine. Alternatively, V_(W)can be determined empirically or via computer modeling for eachapplication and input as a constant into the control circuit 702.

The flow output from this device must be resolved to provide F_(W/CB)and F_(W/C) and F_(B). In chamber pressure control applications it mayalso be necessary to provide and control a ratio of gases as the flowfrom F_(W/CB)′ may be the sum of two or more flow controllers. Thefollowing are examples of considerations that must be made whenresolving these flows:

-   -   F_(W/CB)=F_(W/CB)′−TFDS; where TFDS is the transient flow into        V_(DS) associated with changes in pressure in V_(DS) and is a        function of V_(DS) and dP_(DS)/dt and governed by PV=nRT.        F_(W/CB)′ must not be impacted by changes in pressure upstream        of the flow sensor and is a function of dP_(US)/dt.    -   F_(W/C)=F_(W/CB)−F_(B)−TFW; where F_(B) is the bleed flow        through the restrictor R_(B) and TFW is the transient flow in        V_(W) associated with changes in pressure in V_(W) and is a        function of V_(W) and dP_(WB)/dt. TFW may be ignored and the        need for Pwb may be eliminated if Vw can be made small enough        such that these values are negligible when compared to Fw/c.    -   F_(B) is only a function of P_(WB) when P_(WB)>2P_(D) (i.e.        chocked flow) because R_(B) is designed such that during these        conditions (P_(WB)>2P_(D)), the flow F_(B) is chocked. F_(B) is        characterized as a function of P_(WB) in production to account        for any variation in manufacturer of R_(B). F_(B) may be zero in        chamber pressure control application where F_(W/C) is relatively        large.        where:

-   V_(W) is a volume between the R_(W), the bleed restrictor (R_(B)),    and the control valve 706;

-   R_(F) is the effective restriction of flow sensing technology; and

-   F_(W/CB) is the sum of the flow R_(B) through the bleed restrictor;    the flow Fw/c through the total effective restriction to the    chamber, and the transient flow into V_(W) associated with changes    in pressure (dP_(WB)/dt).

FIG. 8 is a simplified schematic of another embodiment of a gas deliverysystem 800 of the invention coupled to a processing chamber 150. The gasdelivery system 800 is essentially identical to the system 600 describedabove, except wherein a flow sensor 812 is positioned downstream of thebypass control branch 218 with pressure sensors 822, 824 positioned todetect the pressure on the immediate upstream and downstream sides ofthe flow sensor 812. Although the bypass control branch 218 is shownteed between the pressure sensor 822 and the control valve 212, thebypass control branch 218 may be positioned in other positionsdownstream of the control valve 212.

In this embodiment, the first pressure sensor 822 is necessary formeasuring the pressure P_(US) upstream of the flow sensor 822 to ensurethe flow sensor 812 output is accurate during upstream pressureperturbations, including flow changes through the bypass control branch218, are accurately reported by the flow sensor 812. The first pressuresensor 822 is utilized to resolve the flow through the bypass restrictor230. Bleed flow through the restrictor 230 is chocked as describedabove. The F_(W/C) may be resolved as described with reference to theembodiment of FIG. 7.

The following are examples of considerations that must be made whenresolving these flows in a device which has the flow sensor downstreamof the control valve and downstream of the branch to the bleedrestrictor:

-   -   F_(W/CB)=F_(W/C)′+F_(B)−TFUS where F_(B) is the bleed flow        through the restrictor R_(B). TFUS is the transient flow into        V_(US) associated with changes in pressure in V_(US) and is a        function of V_(US) and dP_(US)/dt and governed by PV=nRT.        F_(W/C)′ must not be impacted by changes in pressure upstream of        the flow sensor and is a function of dP_(US)/dt.    -   F_(W/C)=F_(W/C)′−TFDS; where TFDS is the transient flow in        V_(DS) associated with changes in pressure in V_(DS) and is a        function of V_(DS) and dP_(DS)/dt.    -   F_(B) is only a function of P_(US) when P_(US)>2P_(B) (i.e.        chocked flow) because R_(B) is designed such that during these        conditions (Pus>2PB) flow F_(B) is chocked. F_(B) is        characterized as a function of P_(US) in production to account        for any variation in manufacturer of R_(B).

Thus, gas delivery systems having control circuit that advantageouslyenable characterization of the heat transfer conditions between thesubstrate and substrate support have been provided. The innovativecontrol circuits enable the determination of the pressure and flow ratesof gas flowing to the backside of the substrate. Accuracy of backsidegas flow control has been improved over the state of the art. Moreover,quick and efficient purging of the control circuit and passages leadingto the substrate support is enabled. It is also contemplated that thegas delivery system may be configured to supply gas to other aspects ofthe processing system. For example, the gas delivery system may beutilized to at least partially regulate or control chamber pressures, orto deliver at least one of process gases, purge gases, cleaning agents,or carrier gases among others.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. Apparatus for gas control, comprising: at least a first flow sensorhaving an inlet adapted for coupling to a gas supply by a first gasline; a control valve; a second gas line coupled to an outlet of theflow sensor and an inlet of the control valve; a third gas line coupledto an outlet of the control valve; a upstream pressure sensor coupled tothe first gas line and adapted to sense a metric indicative of pressurewithin the first gas line; and a downstream pressure sensor coupled tothe third gas line and adapted to sense a metric indicative of pressurewithin the third gas line.
 2. The apparatus of claim 1 furthercomprising: a bypass line coupled to the third gas line.
 3. Theapparatus of claim 2, wherein the bypass line further comprises: arestrictor sized such that flow is choked and proportional to thedownstream pressure sensor; and a bypass valve coupled in parallel. 4.The apparatus of claim 3 further comprising: a vacuum source coupled inparallel to outlets of the restrictor and bypass valve.
 5. The apparatusof claim 4, wherein the vacuum source provides a pressure at least 2times less than a pressure in the third gas line.
 6. The apparatus ofclaim 1 further comprising: an intermediate pressure sensor adapted toprovide a metric of pressure in the second gas line, wherein a flow ofgas passing through the second gas line may be expressed as:$F_{A} = {F_{S} + {F_{\Delta\quad P_{S}}\left( {\frac{\mathbb{d}P_{S}}{\mathbb{d}t},V_{s}} \right)} - {F_{P}\left( \frac{\mathbb{d}P}{\mathbb{d}t} \right)}}$where: F_(S) is the flow sensed by the flow sensor; P is the pressuresensed in the first gas line; P_(S) is the pressure sensed in the secondgas line; and V_(S) is the volume between flow sensor and the controlvalve in the second gas line.
 7. The apparatus of claim 6 furthercomprising: a bypass control branch teed to the third gas line andhaving a bypass restrictor; a bypass valve coupled in parallel to thebypass restrictor; and a vacuum source coupled in parallel to outlets ofthe bypass restrictor and the bypass valve.
 8. The apparatus of claim 1further comprising: an intermediate pressure sensor coupled to thesecond gas line and adapted to sense a metric indicative of pressurewithin the second gas line and;
 9. The apparatus of claim 8, wherein aflow of gas passing through an outlet of the apparatus downstream of thedownstream pressure sensor may be expressed as:F _(W) =F _(A) −F _(BLEED)(P _(W)) where: F_(A) is the flow measured bythe flow sensor; F_(BLEED) is the flow to the vacuum source; and P_(W)is the pressure sensed in the third gas line
 10. The apparatus of claim9, wherein the flow of gas to the vacuum source is at least one ofmeasured or factory calibrated.
 11. The apparatus of claim 2, whereinthe bypass line is disposed downstream of the downstream pressuresensor.
 12. The apparatus of claim 2 further comprising: a bypasspressure sensor coupled to the bypass control branch and adapted tosense a metric indicative of pressure within the bypass control branch.13. The apparatus of claim 1, wherein the third gas line is coupled to aprocessing chamber.
 14. The apparatus of claim 16, wherein the third gasline is routed through a substrate support disposed in the processingchamber.
 15. The apparatus of claim 1, wherein the control valve, theflow sensor, and up to three pressure sensors define a first sub-circuithaving a first gas outlet; and a second sub-circuit configuredsubstantially identical to the first sub-circuit and having a second gasoutlet.
 16. The apparatus of claim 15, wherein the outlet of the firstsub-circuit is coupled to a first substrate support and the outlet ofthe second sub-circuit is coupled to a second substrate support.
 17. Theapparatus of claim 16, wherein the first substrate support is disposedin a different processing chamber than the second substrate support. 18.The apparatus of claim 16, wherein the outlet of the first sub-circuitis coupled to a first backside gas control zone of the first and secondsubstrate supports; and the outlet of the second sub-circuit is coupledto a second backside gas control zone of the first and second substratesupports.
 19. Apparatus for gas control, comprising: at least a firstcontrol valve having an inlet adapted for coupling to a gas supply; aflow sensor coupled to an outlet of the control valve; a first gas linecoupled to an outlet of the control valve and the inlet of the flowsensor; a upstream pressure sensor couple to the first gas line andadapted to sense a metric indicative of pressure within the first gasline. a second gas line coupled to an outlet of the flow sensor; and adownstream pressure sensor coupled to the second gas line and adapted tosense a metric indicative of pressure within the second gas line. 20.The apparatus of claim 19 further comprising; a restrictor disposed inthe second gas line; an intermediate pressure sensor coupled to thesecond gas line and adapted to sense a metric indicative of pressurewithin the second gas line upstream of the restrictor;
 21. The apparatusof claim 19 further comprising: a bypass line coupled to the second gasline down stream of the restrictor.
 22. The apparatus of claim 21,wherein the bypass line further comprises: a bypass restrictor; and abypass valve coupled in parallel.
 23. The apparatus of claim 22 furthercomprising: a vacuum source coupled in parallel to outlets of therestrictor and bypass valve.
 24. The apparatus of claim 23, wherein thevacuum source provides a pressure at least 2 times less than a pressurein the second gas line.
 25. The apparatus of claim 24 furthercomprising: an intermediate pressure sensor adapted to provide a metricof pressure in the second gas line, wherein a flow of gas passingthrough the first gas line may be expressed as:$F_{A} = {F_{S} + {F_{\Delta\quad P_{S}}\left( {\frac{\mathbb{d}P_{S}}{\mathbb{d}t},V_{s}} \right)} - {{Fpu}\left( {\frac{\mathbb{d}{Pu}}{\mathbb{d}t},{Vu}} \right)}}$where: F_(S) is the flow sensed by the flow sensor; Pu is the pressuresensed in the first gas line; Vu is the volume between the between theflow sensor and the control valve in the first gas line; P_(S) is thepressure sensed in the second gas line; and V_(S) is the volume betweenflow in the second gas line.
 26. The apparatus of claim 25 furthercomprising: a bypass control branch teed to the second gas line; abypass restrictor; a bypass valve coupled in parallel to the bypassrestrictor; and a vacuum source coupled in parallel to outlets of thebypass restrictor and bypass valve.
 27. The apparatus of claim 26,wherein a flow of gas passing through an outlet of the apparatus teed tothe second gas line and bypass line may be expressed as:F _(W) =F _(A) −F _(BLEED)(P _(W)) where: F_(A) is the flow measured bythe flow sensor; and F_(BLEED) is the flow to the vacuum source.
 28. Theapparatus of claim 27, wherein the flow of gas to the vacuum source isat least one of measured or factory calibrated.
 29. The apparatus ofclaim 27 further comprising: a restrictor disposed in the second gasline; and an intermediate pressure sensor coupled to the second gas lineand adapted to sense a metric indicative of pressure within the secondgas line upstream of the restrictor.
 30. The apparatus of claim 22further comprising an outlet gas line.
 31. The apparatus of claim 30,wherein the outlet gas line is coupled to a processing chamber.
 32. Theapparatus of claim 19, wherein the control valve, the flow sensor, theupstream pressure sensor and the downstream pressure sensor define afirst sub-circuit having a first gas outlet; and a second sub-circuitconfigured substantially identical to the first sub-circuit and having asecond gas outlet.
 33. The apparatus of claim 32, wherein the outlet ofthe first sub-circuit is coupled to a first substrate support and theoutlet of the second sub-circuit is coupled to a second substratesupport.
 34. The apparatus of claim 32, wherein the first substratesupport is disposed in a different processing chamber than the secondsubstrate support.
 35. The apparatus of claim 33, wherein the outlet ofthe first sub-circuit is coupled to a first backside gas control zone ofthe first and second substrate supports; and the outlet of the secondsub-circuit is coupled to a second backside gas control zone of thefirst and second substrate supports.
 36. The apparatus of claim 19further comprising: a restrictor disposed between the second anddownstream pressure sensor.
 37. The apparatus of claim 19 furthercomprising: a bypass control branch teed between the control valve andthe flow sensor; a bypass restrictor; a bypass valve coupled in parallelto the bypass restrictor; and a vacuum source coupled in parallel tooutlets of the bypass restrictor and bypass valve.